This shirt is a secret handshake. It lets other Time Agents know you are working together. This shirt along with a well-executed head nod says, "FOLLOW ME INTO THE SHADOWS. IT IS TIME TO CONSPIRE."
"Men's" sizes are all super-comfy lightweight American Apparel. "Women's" sizes are equally comfy Alternative Apparel. Gender, like time and your own sense of self as based on your memories, is a construct. Wear whichever shirt best fits your body.